Originally Posted by
Vessbot
Earlier I posted the same thing, that over time it should align itself with "cabin gravity" since that's the only up/down reference it knows. But after a quick bit of research I changed my mind and deleted it. Because the pendulous vanes are on the gyro case itself, i.e., the innermost part of the instrument that stays fixed in space, inside of all the airplane's free motions around it. So, let's say you're flying North and concerned with rigidity and errors while banking left or right... as far as the inner case, you shouldn't think of it as banking left or right, but rather banking West or East, because it's gonna (mostly) stay fixed in space.
If you start a right turn, the "cabin gravity" banks East (referencing the up direction of it, not down)
I think you're correct but misunderstanding how the 'cabin gravity' affects the vanes. In a 360 degree perfectly coordinated turn each of the pendulous vanes will open and close according to a sinusoidal pattern with each vane's degree of openness being 90 degrees out of phase with the next one. The outcome is a _constant_ force which rotates around the axis of the gyroscope's spin. The force is located below the gyroscope's center of gravity. The outcome - as far as I can see - is a constant force acting to push the base of the gyroscope into a position which results in an equal force being applied by all the vanes. In level flight that will result in zero vane motion over time. In a coordinated turn that will (eventually) result in the equal opening of each vane in turn once the gyroscope has become aligned with cabin gravity - different vanes will open as the aircraft adopts a heading of 90, 180, etc as the gyroscope remains fixed in position. With the turn being coordinated, once the gyroscope has become aligned with cabin gravity the changing bearing of the turn manifests only as yaw, and single axis vertical-rotating gyroscope is not affected by yaw so the bearing component of the turn has no overall effect.
That's probably not very well explained.